by Laura Petrecca, USA TODAY

by Laura Petrecca, USA TODAY

At least 39 people were killed during a Saturday afternoon shooting rampage at a shopping mall in an upscale district of Nairobi. The attack is believed to be orchestrated by extremists against non-Muslim Kenyans and Westerners in the area.

At least 150 were also injured, says Kenyan President Uhuru Kenyatta, who also reported the current death toll. He said he lost some family members in the attack

Somali militant group al-Shabaab claimed responsibility on Twitter for the deadly shooting, which was allegedly carried out by five to 10 gunmen with AK-47s and other sophisticated weapons. Al-Shabaab said the attack was retribution for Kenyan forces' 2011 push into Somalia and threatened more violence.

"The Mujahideen entered #Westgate Mall today at around noon and are still inside the mall, fighting the #Kenyan Kuffar inside their own turf," the group said on Twitter.

"What Kenyans are witnessing at #Westgate is retributive justice for crimes committed by their military," the group said.

Early Sunday morning, 12 hours after the attack began, gunmen remained holed up inside the mall with an unknown number of hostages. Kenyatta called the security operation "delicate" and said safeguarding hostages was a top priority.

Americans were among those injured at the Westgate mall shooting, according to a statement from Marie Harf, deputy spokesman for the State Department.

"We have reports of American citizens injured in the attack, and the U.S. Embassy is actively reaching out to provide assistance," she said. "Due to privacy considerations, we have no further comment on American citizens at this time." No Americans were reported killed.

Two Canadians, including a diplomat, were among the dead, according to the prime minister's office. French authorities said two French women were killed.

In a separate statement, a White House spokeswoman said some staff at the U.S. Embassy in Kenya have been "tragically affected" by the attack. No other information was provided.

"The perpetrators of this heinous act must be brought to justice, and we have offered our full support to the Kenyan Government to do so," Caitlin Hayden, a spokeswoman for the White House National Security Council, said in the statement

The attack began on Saturday afternoon, according to Kenya's Daily Nation. Gunmen tossed grenades and opened fire as panicking shoppers fled the building, some jumping down one story from the second floor of the mall to escape, witnesses told the paper.

Witnesses told local and national news media that the gunman asked Muslims to leave before opening fire. Kenya is 83% Christian with a sizable Muslim community - about 11% of its 44 million people.

The gunmen carried AK-47s and wore vests with hand grenades on them, Manish Turohit, 18, who hid in a parking garage for two hours, told the Associated Press.

"They just came in and threw a grenade. We were running and they opened fire. They were shouting and firing," he said after marching out of the mall in a line of 15 people who all held their hands in the air.

As night fell in Kenya's capital, hostages remained inside the mall, but officials didn't say how many people were held captive. Army special forces troops had moved inside the mall as well.

Off-duty Sgt. Major Frank Mugungu told the AP that he saw four male attackers and one female, and that he could clearly identify one of the gunmen as a Somali, though he could not identify the rest.

Military cordoned off the building in the heart of the upscale Westlands district, which is home to upper-class Kenyans and expatriate Westerners - many of whom work for the United Nations - and a locale frequented by tourists.

A local organization was hosting a party for children at the Israeli-owned Westgate mall on Saturday. The mall is also a popular nightspot for hip, young Kenyans who gather there to watch movies or eat at restaurants there.

It is on Kenya's watch list as a site for attacks, along with its towering conference center and Western hotels such as the Hilton.

Like most shopping mall complexes in Nairobi, it is manned by security personnel at its entrance, checking bags and shoppers with metal detectors. But locals noted repeatedly in the aftermath of the attacks that these are just cursory checks and that the security guards are no match for armed gunman.

Still, security in the city is tight because of prior attacks in the past two decades, including one on the U.S. Embassy by al-Qaeda in 1998 that killed more than 200 people. Besides the threat of terrorism, the city faces its own internal threats - sometimes called "Nairobbery" - arising from extreme poverty and income inequality.

Crime and corruption are among the biggest concerns of the locals. The city is one of the most dangerous urban areas in sub-Saharan Africa. Although the situation is better than a decade ago, most middle-class and wealthy urban dwellers refrain from walking on city streets after dark, a situation that has led to the popularity of the city's shopping malls in its rich western districts as quasi-entertainment centers.